/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.CollectPreconditions.checkEntryNotNull;

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.concurrent.LazyInit;
import com.google.j2objc.annotations.RetainedWith;
import java.util.function.BiConsumer;
import javax.annotation.Nullable;

/**
 * Implementation of {@link ImmutableMap} with exactly one entry.
 *
 * @author Jesse Wilson
 * @author Kevin Bourrillion
 */
@GwtCompatible(serializable = true, emulated = true)
@SuppressWarnings("serial") // uses writeReplace(), not default serialization
final class SingletonImmutableBiMap<K, V> extends ImmutableBiMap<K, V> {

    final transient K singleKey;
    final transient V singleValue;

    SingletonImmutableBiMap(K singleKey, V singleValue) {
        checkEntryNotNull(singleKey, singleValue);
        this.singleKey = singleKey;
        this.singleValue = singleValue;
    }

    private SingletonImmutableBiMap(K singleKey, V singleValue, ImmutableBiMap<V, K> inverse) {
        this.singleKey = singleKey;
        this.singleValue = singleValue;
        this.inverse = inverse;
    }

    @Override
    public V get(@Nullable Object key) {
        return singleKey.equals(key) ? singleValue : null;
    }

    @Override
    public int size() {
        return 1;
    }

    @Override
    public void forEach(BiConsumer<? super K, ? super V> action) {
        checkNotNull(action).accept(singleKey, singleValue);
    }

    @Override
    public boolean containsKey(@Nullable Object key) {
        return singleKey.equals(key);
    }

    @Override
    public boolean containsValue(@Nullable Object value) {
        return singleValue.equals(value);
    }

    @Override
    boolean isPartialView() {
        return false;
    }

    @Override
    ImmutableSet<Entry<K, V>> createEntrySet() {
        return ImmutableSet.of(Maps.immutableEntry(singleKey, singleValue));
    }

    @Override
    ImmutableSet<K> createKeySet() {
        return ImmutableSet.of(singleKey);
    }

    @LazyInit
    @RetainedWith
    transient ImmutableBiMap<V, K> inverse;

    @Override
    public ImmutableBiMap<V, K> inverse() {
        // racy single-check idiom
        ImmutableBiMap<V, K> result = inverse;
        if (result == null) {
            return inverse = new SingletonImmutableBiMap<V, K>(singleValue, singleKey, this);
        } else {
            return result;
        }
    }
}
